328 Dr. C. F. Lutkeii on Spontaneous 



terids— namely, in Aster ias prohlema^ Stp. {alhula, Stimps.), 

 and A. tenuispina^ Lamk., and in some forms allied to these 

 two species. In common with the fissiparous Ophiurids they 

 have normally more than five arms ; but this furnishes no 

 ground for supposing that other Asterids with six or more 

 tlian six arms have some tendency to division ; indeed we 

 have examples to the contrary in the Solasteres with many 

 arms, and in the six-armed Asterias polaris^ neither of which 

 presents the least traces of this mode of reproduction. What 

 strikes us immediately in looking at a series oi A. tenuispina 

 and prohhma is, that a great many of them have the arms 

 unequally developed, and that the shorter and weaker arms 

 form on one side a separate group, as if they had been deve- 

 loped after the others, which no doubt is the case. MM. Steen- 

 strup*, Sarst, HiickelJ, and Von Martens§ have already de- 

 voted special attention to the former species ; but I will, not- 

 withstanding, communicate the result of my own observations. 

 Of 23 specimens 11 (with seven to ten arms) have incontest- 

 able traces of a regeneration of three to seven (most frequently 

 four) arms: the smallest of these 11 specimens is \\ inch in 

 diameter ; the largest, if the weaker (younger) side were as 

 much developed as the other, would measure 5^ inches. The 

 smaller the specimens the more clearly in general do we see 

 that a regeneration of this kind (and the previous division ?) has 

 taken place : of 15 specimens less than 4 inches in diameter, 

 9 are in this condition ; whilst of 8 which vary in diameter 

 from 4 to 7 inches, there are only 2. In the other 12 speci- 

 mens (of the 23) the arms are either (approximately) of the 

 same length, or the number of shorter ones does not exceed 

 one or two, and the existence of a single arm shorter than the 

 others indicates nothing more tlian an accident which is very 

 common in all starfishes, namely that one or more of the arms 

 may have been broken or torn away and regenerated. The 

 series of specimens tliat I have examined does not indicate 

 that this division and regeneration, perhaps frequently re- 

 peated, must result in the number of arms in the larger and 

 more developed individuals being on the average either greater 

 or less than in the young individuals i|. 



* Forliandl. ved de Slcand. Natiuforsk. syvende Mode i Christiania 

 (18.57), pp. 229 et seq. 



t Bidrag til Kundskaben om Middelhavets Littoralfaiina, ii. p. 108. 



X Generelle Moi-phologie (1866), i. p. 3-50. 



§ Archiv fiir Naturg. xxx. 1, p. (SS. 



II See also some remarks by M. R. GreefFon the Asterids of the Canaries, 

 and among others Aster ins teviiisputa. He says it is "woi-thy of remark 

 tliat on the rocky shore < xp srd to the action of the breakers, we scarcely 

 meet with any but small and irregular specimens, whilst far irom tlie 



